Coil tightener

ABSTRACT

Coil tightening and tying system provides a strap loop having overlapping end portions in circling relation to the coil, establishes travel-retarding engagement of strap at a single intermediate location between the ends of the loop, shrinks the portion of the loop between one of the end regions and the circumferential location into gripping contact with the outer coil convolution, and produces relative rotary movement between the coil and the strap of the loop in a direction to rotate the outer convolution of the coil in a volute direction while maintaining the engagement to maintain gripping contact with the outer convolution.

United States Patent Johnson 1 May 16, 1972 [54] COIL TIGHTENER PrimaryExaminerBilly .l. Wilhite [72] Inventor. Robert A. Johnson, Flossmoor,Ill. Atwmey wi"iam P- Porcel [73] Assignee: Interlake Steel Corporation,Chicago, lll.

[57] ABSTRACT [22] Filed: June 23, 1970 Appl. No.: 49,047

References Cited UNITED STATES PATENTS 4/1967 Lems 100/3 Coil tighteningand tying system provides a strap loop han'ng overlapping end portionsin circling relation to the coil, establishes travel-retardingengagement of strap at a single intermediate location between the endsof the loop, shrinks the portion of the loop between one of the endregions and the circumferential location into gripping contact with theouter coil convolution, and produces relative rotary movement betweenthe coil and the strap of the loop in a direction to rotate the outerconvolution of the coil in a volute direction while maintaining theengagement to maintain gripping contact with the outer convolution.

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SHEET M []F 5 con. TIGI-ITENER BACKGROUND OF THE INVENTION The presentinvention relates to the art of strapping apparatus and moreparticularly to strapping machines of the type capable of tightening aspiral coil and applying a strap loop about the tightened coil.

The technique of using the binder strap or band as the coilgrippingelement during the coil-tightening operation is taught in U.S. Pat. No.3,320,874. Specifically, as disclosed in that patent, a strap loop isestablished snug upon the outer coil wrap or convolution and is rotatedin a volute direction to impart corresponding movement of the outer coilconvolution, thereby drawing the inner coil convolutions taut.Simultaneously, the strap of the loop is taken up to shrink the binderstrap to maintain its snug engagement with the outer coil convolution asthe coil shrinks. Rotation of the strap loop and, hence, the outer coilwrap is accomplished by moving the strapping head in an arcuate pathabout the coil periphery.

Instead of rotating the strapping head to effect the rotation of theloop in a volute direction, the head can remain fixed, and rotation ofthe strap loop in snug contact with the outer coil convolution can beproduced by drawing tensioned band about the coil from a strapreservoir.

SUMMARY OF THE INVENTION The present invention relates to improved coiltightening and tying system of the latter type.

In accordance with a principal feature of the present invention, alength of band is fed by a strapping head and is looped inloosely-encircling relation about a coil. A hold-back mechanism thatincludes a traction wheel having controlled resistance to rotationengages the band of the loop at a single intermediate position betweenthe opposite ends of the loop. The traction wheel cooperates with thestrapping head during retraction of band by the head to preventretraction of a predetermined segment of the length of band comprisingthe loop and to cause the remaining band of the loop to be shrunk intosnug engagement with the outer coil convolution. When the retractionforce on the strap produced by the head exceeds the preset resistance torotation of the traction wheel, the traction wheel rotates to allow bandof the restrained loop segment to be retracted so that the band of theloop rotates in clamping contact with the outer coil convolution in avolute direction to thereby draw the inner convolutions taut.

In the preferred embodiment shown herein, the traction wheel is affixedto the shaft of a hydraulic motor which is connected in a closedhydraulic circuit to a hydraulic reservoir through an adjustable flowcontrol and release-valve arrangement.

A more specific but important feature of the present invention residesin the provision of mechanism cooperable with the head to configure thelength of band that is fed into a loop of generally-keyslot shape,characterized by a generally circular main loop region that encircles amajor peripheral region of the coil and a generally U-shaped open-bubbleregion which bulges outwardly from the coil and joins the main loopregion. The traction wheel engages band at one extremity of the bubbleregion. During the coil-tightening operation, the band of the main loopregion is shrunk into engagement with the coil and, subsequently, thetraction wheel rotates to allow movement of band from the bubble regionto the main loop region to effect coil-tightening rotation of the outercoil convolution. As the coil is tightened, the band of the bubbleregion progressively collapses upon the coil.

In the strapping system of the present invention, the strapping head andholdback mechanism are mounted to pivot in unison above ahorizontally-movable carriage. Tangency-sensing mechanism controlspivotal movement of the head and hold-back mechanism to maintain thehead tangent with respect to the coil periphery throughout thecoil-tightening operation thereby to insure maximum tightening of thecoil.

Other features and advantages of the invention will be apparent from thefollowing description and claims and are illustrated in the accompanyingdrawings which show structure embodying preferred features of thepresent invention and the principles thereof, and what is now consideredto be the best mode in which to apply these principles.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of atypical strapping station incorporating the coil-tightening system ofthe present invention;

FIG. 2 is a top-plan view of the horizontal carriage and showing thepresently-preferred structural arrangement for mounting the hold-backmechanism and strapping head;

FIG. 3 is a front-elevational view, partly in section, furtherillustrating the mounting structure for supporting the holdbackmechanism and strapping head on the horizontal carrlage;

FIGS. 4 and 5 are perspective views showing the hold-back mechanism andstrapping head positioned adjacent a coil;

FIG. 6 is a detailed fragmentary view of the hold-back mechanism showingthe pinch-roll mechanism, accumulator void and hydraulic motor;

FIG. 7 is a top-plan view of the pinch-roll assembly;

FIG. 8 is a sectional view taken as indicated along 88 of FIG. 7;

FIGS. 9 and 10 are fragmentary sectional views of the gated-guide tracksegment; and

FIGS. 11 and 12 are diagrammatic views illustrating the keyslot shapedstrap-loop formed in accordance with the invention and the manner ofobtaining a coil-tightening capstan effect through operation of thehold-back mechanism.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The invention relatesto a system for forming a strap loop directly upon a coil and utilizingtensioning of the loop for tightening the coil. For purposes ofdisclosure, the invention is illustrated in a conventional strappingstation, such as that shown in Winkler U.S. Pat. No. 3,252,408, andGasper, et al., U.S. Pat. No. 3,320,874.

The principal features of the strapping station are described here toprovide proper environment for understanding the operation of thestrapping system of this invention, but it should be understood that thepresent system has application apart from the specific arrangementsshown herein.

Referring to FIG. 1, the strapping machine 1 in which the invention isshown embodied consists of two bases, 2 and 3; the base 2 supports twocorner posts 4 and 5, while the base 3 supports two corner posts 6 and7. An l-beam 8 is connected between the upper ends of the two posts 4and 5, while another I-beam 9 is connected across the upper ends of thetwo posts 6 and 7. Mounted between the posts 4 and 5 at the upper end isanother I-beam 10. Similarly mounted between the posts 5 and 7 at theirupper ends is another I-beam 11. A carriage 12 is mounted for verticalmovement between the posts 4 and 5 and is supported by two chains 13 and14 which are driven by means of sprockets at 15 attached to a shaft 16.Likewise, a carriage 17 is mounted for vertical movement between the twoposts 6 and 7, and is supported by means of two chains 18 and 19 drivenby means of two sprockets at 20 geared to the shaft 16. The shaft 16 isdriven in one direction or another by means of a motor 21 suitablymounted on a platform 22 secured to the post 7. Y

The chains 13 and 14 are connected at their opposite ends to acounter-weight 23 which is guided along the post 5. In a similar manner,the opposite ends of the chains 18 and 19 are secured to anothercounter-weight 24 guided along the corner post 7. With this arrangement,rotation of the shaft 16 by the motor 21 in one direction causes bothcarriages l2 and 17 to be lowered together, while rotation of the shaft16 by the motor 21 in the opposite direction causes both carriages I2and 17 to be elevated.

The carriage 17 supports a horizontal slide carriage 26 which is mountedfor movement toward and away from the object to be strapped on the twoend plates 17A and 17B of the carriage 17. Each of the end plates isprovided with a plurality of outboard rollers 17C positioned to rollalong the vertical post members 6 and 7 to maintain positional stabilityof the carriage 17 as it is raised or lowered by the chains 18 and 19.Additionally, plates 17A and 17B are provided with inboard rollers 17Darranged in the two horizontal rows which receive and guide the siderails 26R of the slide carriage 26 and permit movement of the carriagethrough a predetermined path in a horizontal plane. The carriage 26 isstabilized by front and rear cross-brace structures 26A and 26B (FIG.2), each rigidly connected to each of the side rails 26R.

As will be described in detail below, the horizontal slide car riage 26carries a strapping head 25 and a hold-back mechanism H. The strappinghead 25 can be of many types, but 'one particularly suited for such astructure is shown in U.S. Letters Pat. No. 3,120,171, which was issuedon Feb. 4, 1964, in the name of M. B. Hall, et al. Such a strapping headautomatically feeds a length of strap from a supply source, permits thelength of strap to be encircled into a strap loop, automatically shrinksthe strap loop onto an object, and secures the overlapping ends of thestrap loop together and severs the strap loop from the supply source.

A strap guide segment 27 carried on the strapping head 25 is positionedvertically by movement of the carriage l7, and a correspondingstrap-guide segment 30 is positioned vertically by movement of thecarriage 12. The carriages 12 and 17 move in synchronism between anupper position wherein the strap guide segments 27 and 30 are in acommon horizontal plane with strap guide segments 28 and 29, and a lowerposition which is pictured in FIG. 1. As will be described, the systemof the present invention incorporates a gated-guide track segment 101which is permanently affixed in alignment with strap-guide segment 29and which, together with guide segments 27, 28, 29 and 30, cooperativelydefine a generallycircular continuous path guideway or chute beginningand ending at the strapping head 25. The strapping head 25 is operableto feed strap through this guideway to form a closed circular loop ofstrap at the elevated position. As described in the aforesaid Gasper, etal., U.S. Pat. No. 3,320,874, after the coil is in proper position, andafter the strap loop is formed, the carriages l2 and 17 descend to lowerthe loop of strap to a position illustrated in FIG. 1 to encircle atmid-height region of the coil. Concurrently, the strapping head 25 ismoved toward the coil on the horizontal slide carriage 26.

Referring to FIGS. 2 and 3, the supporting structure for the strappinghead 25 and hold-back mechanism H includes a lower mounting plate 50having a pair of oppositely-extending arms 50A and 50B and anoutwardly-projecting V-shaped central body portion 50C that is affixedrigidly to the horizontal carriage 26, such as by directly welding theunderside of v the V-shaped main body portion 50C to the carriagecrossbar 26B and by connecting the terminal end arm 50A to the carriagecrossbar 26A by a bolt 52. A bearing support plate 54 is welded to thelower mounting plate 50 to mount a bearing block 56. A strapping headsub-plate 58 is pivotly supported above mounting plate 50 at a pivotpoint A in a manner to be described in greater detail below and isadditionally supported by bearing block 56 so that it is free to rotateabout pivot point A above the mounting plate 50. As will be described,rotation of the strapping head subplate 58 is controlled by a cylinder60 that has its rear end 60A pin-mounted to carriage crossbar 26Athrough mounting plates 62 and 64, and which has its piston rod 608drivingly connected to sub-plate 58 through clevis 66.

A tangency-sensing element B (FIGS. 2, 3 and 4) is mounted in rotatablerelation between the plates 50 and 58 at the pivot point A. The sensingelement B includes a central vertical hub 67 that is journaled on apivot shaft 67A which had its opposite ends carried in the plates 50 and58. They sensing element B has a forwardly diverging cam arm 67Bradiating from the hub 67 carrying a pair of cam rollers 68,

cam

normally located in partially-projecting relation through the open-frontface of the tangency-sensing unit B. Finally, the sensing element B hasa sidewise-radiating switch-actuating arm 67C centered between a pair oflimit switches 60 and 62 that are fixed to the plate 58.

The strapping head 25 is mounted to sub-plate 58 so that the center lineof rotation of the tangency-sensing assembly B coincides with the centerline of sealer jaws 25.] of the head 25. When the head 25 is tangent tothe coil periphery, the rollers 68 engage the coil evenly and theactuating arm 67C remains centered between the limit switches 60 and 62.When the head 25 inclines a predetermined extent from tangency in eitherdirection, the rollers 68 sense the change and cause the actuating arm67C to operate a corresponding one of the limit switches 60 and 62 foradjusting the head position through the action of cylinder 60 effectingrotation of the strapping head sub-plate 58. I

The above-mentioned hold-back mechanism H is similarly mounted on thestrapping head sub-plate 58. Basically, the hold-back mechanism Hconsists of a hydraulic motor M on whose shaft is mounted a tractionwheel 70. As will be described, the motor M is connected in a closedhydraulic circuit to a hydraulic reservoir 72 through an adjustable flowcontrol and release valve arrangemenLThe traction wheel 70 is located toalign with a void space 74 between a pair of spaced plates 76 and 78which are mounted in spaced parallel relation above sub-plate 58 bymeans of spacer rods 80, 81. This alignment is also coincident with thestrap track section 90 and the track assembly 91 mounted to thestrapping head 25 (FIGS. 4 and 5), and the strap guide segment 27 whichguides the band from the strapping head to the first overhead tracksection 30.

As best shown in FIGS. 6 to 8, a pinch-roll assembly 82 works inconjunction with the traction wheel 70 and includes an idler wheel 83swingable between an upright position facing the traction wheel and aretracted position (shown in dotted line indicated at 83 in FIG. v6)spaced therefrom below plate 78 to accommodate formation and collapse ofthe bubble portion of the strap loop, as will be described hereinbelow.

The sub-plate 58 serves to support the pinch-roll assembly 82 and, forthis purpose, includes an upstanding support 86 (FIGS. 7 and 8) alongwhich a plate clevis 92 (FIG. 7) is secured by means of bolts 86B. Acradle-like frame 84, generally L-shaped in plan elevation (see FIG. 7),is pivoted on a vertical pin 94 which is supported between integralwings 92W of the plate clevis 92. As shown in FIG. 7, arectangularsleeve structure 96 is secured to the edge of the cradle 84and includes a pair of flange bearings 98 that mount a shaft 100 forrotation about a horizontal axis 100H, which is located beneath theplane of the plate 78 that serves as the bottom boundary of the voidspace 74. The shaft 100 carries-a radially-projecting arm structure 102which mounts the idler wheel 83. Rotation of shaft 100 swings the radialarm 102 about the horizontal axis 1001-1 (FIG. 7).

Rotation of shaft 100 is controlled by a cylinder 104 which actuates apiston rod 106. The piston rod 106 carries a clevis 108 at its free end,the clevis being connected to a crank arm 110 by means of a pivot pin108?. The cylinder 104 is provided with side-wise-extending shaft stubs112, 114 swingmounted to the frame 84 by journaling the stubs 112, 114within a flanking pair of depending bearings 116, 118 shown secured tothe frame by bolts 120. To accommodate limited pivotal movement ofcylinder 104, sub-plate 58 (FIG. 6) is cut out as at 122 (FIG. 6), andthe frame 84 is hollowed or recessed as at 124. A positive stoparrangement accurately determines the limit of swinging movement of theidler wheel 83 to permit accurate alignment with the traction wheel 70.The stop arrangement is shown as including outboard plate 126 located atone extremity of the frame 84 and carrying an adjustable set screw 130.A plate 128 is secured to the rectangular sleeve 96 by weld 128W (FIG.7) to mount the outboard plate 126. The set screw 130 is engageable withthe crank arm 1 10 to determine proper orientation of the idler wheel83.

The strap in void space 74 is held against movement by the action of thetraction wheel 70 which is connected in mechanical driving engagementwith the hydraulic pumping circuit (FIG. 11) that functions as thebraking means of the hold-back mechanism H. A gear hydraulic-type motorM is shown in the circuit to effect pumping of hydraulic fluid in thedirection of the arrows when the traction wheel 70 rotates in adirection to accommodate return of strap toward the strap supply. Theresistance to pumping flow and, hence, the braking resistance that themotor M presents to the traction wheel 70 is controlled by a releasevalve RV and a flow control valve CV.

The pinch-roll assembly serves to insure loading of the strap againstthe traction wheel 70 with sufficient force to preclude slippage. Forthis purpose, the frame 84 is normally urged in a clockwise direction asviewed in FIG. 7 by the action of a bias spring 132 which reacts betweenthe stationary clevis plate 92 and the frame 84. In the illustratedarrangement, the bias spring 132 is of the expansion type and is shownmounted in telescoping relation upon a bolt 134. The bolt 134 projectsthrough a clearance opening 136 in plate clevis 92 and is threadedlyengaged in a tapped hole 138 in frame 84 to accommodate lengthwiseadjustment for varying the compression force exerted by the spring 132.In addition, the plate clevis 92 is provided with an adjustable stop 140which determines the limit position of rotation of the frame 84 in orderto gauge the nip between idler wheel 83 and the traction wheel 70 to thethickness of the strap.

OPERATION As stated, when the carriages 12 and 17 are in their upperposition, adjacent ends of the guide segments 27, 28, 29, and 101, arealigned and cooperatively define a generally-circular continuous pathguideway or chute beginning and ending at the strapping head 25. It willbe noted that when the vertical carriage 17 is at the elevated positionand the horizontal carriage 26 is retracted, the gated-guide segment 101covers the accumulator void 74 (FIGS. 1, 9 and 10) and guides the strapbeing fed into the overhead track to the strapping head 25. Thegated-guide segment 101 includes a fixed gate portion 101A and a movablegate portion 1018 which interengage to define a strap guideway 101C. Themovable gate portion 1018 is raised and lowered by means of cylinder146. A limit switch 148 is positioned above the movable gate portion1013 to be activated upon raising of the gate portion 101B.

After strap feed has started and the leading edge of the strap re-entersthe strapping head 25, strap feed stops when the leading end has enteredthe sealer jaws 25.] of the head 25. This leading end of the strap orband is then held by the gripping jaws which signal the gate portion101B to be elevated by cylinder 146 thereby closing switch 148. Closingof switch 148 signals additional strap feed by the strapping head. Sincethe leading end of the band is restrained by the guide segments 27, 28,29 and 30, the band will bubble out from the open-sided track createdwhen gate portion 1013 was raised and into the void space 74(hereinafter called the accumulator void 74) between plates 76 and 78.The duration of this over-feed is controlled by a time delay relay (notshown) and can be adjusted to provide any desired length of strap. Innormal usage, approximately 48 to 60 inches of overfeed is sufficient toprovide for the subsequent coil-tightening function. When the strapenters the accumulator void 74, its presence is sensed by switch 142(FIG. 6) through the action of the pivoted actuator arm 144 being urgedupwardly by the incoming strap. Upon completion of the over-feed, thecylinder 104 is actuated to swing the idler wheel 83 of the pinch-rollassembly 82 upward through opening 78A in plate 78 to the position shownin full lines in FIG. 6. The strap is pinched between the idler wheel 83and the traction wheel 70 on hydraulic motor M.

A unique keyslot configuration of the loop of strap is formed as aresult of raising the gated-guide track segment 101 during strapover-feed. As shown in FIG. 11, the keyslot loop is characterized by agenerally C-shaped main loop region ML and a generally U-shapedopen-bubble region U outwardly projecting therefrom. It will be notedthat the traction wheel 70 of the hold-back mechanism H is intravel-retarding engagement of the strap at a single intermediatecircumferential location C at one extremity of the U-shaped regionbetween the lead end L and the supply strap region SS of the strap loopS.

The closed loop of strap is formed into the keyslot configuration whilethe carriages 12, 17 are elevated. Thereafter, the carriages 12, 17 arelowered to strip the strap from the stationary guide chutes and positionthe loop in loosely-encircling relation about the coil at the lowerphantom-line position indicated in FIG. 1.

When the strap loop is lowered to the position shown in FIG. 1, thecarriage 26 begins to move toward the coil, and the tangency-sensingmechanism B operates to position the sealer jaws of the strapping headin tangency with respect to the coil. During this time, the strappinghead 25 begins to pull slack strap to shrink the portion of the loopbetween the supply strap portion SS and the circumferential location Cinto gripping contact with the outer coil convolution, as shown in FIG.12. The hold-back assembly H at this time prevents movement of strapfrom the U-shaped open-bubble portion U of the loop S. As explained inthe aforementioned patents, when carriage 12 is lowered, support arms 34are caused to be pivoted into contact with the face of the coil. Thisprovides support for the loop portion of band as it is shrunk around thecoil.

The amount of hold-back or restraining force supplied by the tractionwheel 70 on the strap can be varied by adjustment of the closed loophydraulic circuit of the hold-back mechanism H, which is illustrated inFIG. 11. Rotation of the traction wheel 70, (as a result of strap beingdrawn from the U-shaped bubble portion U) turns the motor M causingfluid flow in the directions of the arrows (FIG. 11). The amount offlow, and hence, the resistance of motor M to rotation is controlled byrelease valve RV and flow control valve CV in the closed hydrauliccircuit. In practice, the valves RV and CV are adjusted so as togenerate sufficient rotation resisting force at traction wheel 70 toallow the friction clamping force between the outer coil convolution andthe main loop region to exceed forces on the coil which would operate inopposition to attempted rotation thereof.

When continued pull exerted by the strapping head 25 overcomes amount ofhold-back force generated by the hold-back mechanism I-I, strap iswithdrawn from the bubble portion U, while'the strap in the main loopportion is established in a travelling capstan" effect on the coil.Continued motion of the strap under the influence of these forceseffects a wrapping action on the coil. As the strap continues to moveabout the coil, the open-bubble portion U collapses as shown dotted inFIG. 12.

When the wrapping action has drawn the coil convolutions to theirmaximum tightness, the strap continues to move about the coil to exhaustthe length of strap of the open-bubble portion U. Just prior to totalcollapse of the bubble U, the pivoted switch actuator arm 144 drops dueto the absence of band in the accumulator void 74. This signals cylinder104 to swing the idler wheel 83 to a retracted position beneath the voidspace, releasing the hold on the strap and permitting complete collapseof the bubble region U. The swing of the idler wheel is toward the coilto avoid tangling of the strap being collapsed toward the coil. Theretracing means of the strapping head 25 continues to withdraw strap,thereby quickly taking up slack created by the release until the strapis again tight around the coil. The seal joint is then completed and thestrap sheared by the strapping head, thus completing a tightening andtying cycle.

It should be noted that minimal destructive forces are applied to thestrap during a cycle of operation, so that the strap which is ultimatelybound about the tightened coil retains its original strength anddurability. This results from the fact that the strap is engaged at asingle intermediate location along the strap loop between a rotatabletraction wheel and an idler wheel. Thus, maintenance of the requiredtensioning of the strap during retraction is accomplished withoutsubjecting the strap to destructive bending forces or heating due tofrictional engagement. Moreover, the tensioning can be easily andprecisely controlled through adjustmentof the hydraulic circuit valvesso that destructive sliding of the strap against the outercoilconvulsion is minimized.

The single point engagement technique in accordance with the presentinvention results in the strap loop being in full girth tight engagementwith the coil only after the coil is finally and fully tightened.

Thus, while preferred constructional features of the invention areembodied in the structure illustrated herein, it is to be understoodthat changes and variations may be made by those skilled in the artwithout departing from the spirit and scope of the appended claims.

What is claimed is:

1. In an apparatus for tightening a spiral coil of strap throughrotation of the outer coil convolution in a volute direction, feed meansfor feeding strap, means cooperating with said feed means for formingstrap into a substantially closed strap loop of generally keyslot shapecharacterized by a generally circular main loop region and a generallyU-shaped open bubble region extending outwardly from the main loopregion, retracting means for withdrawing strap of the strap loop, andhold-back mechanism that includes a traction wheel engageable withbraking means having a predetermined resistance to rotation, thetraction wheel being engageable with the strap of the strap loop at asingle intermediate location therealong and cooperable with theretracting means for tensioning strap of the main loop region to effectfriction clamping engagement thereof with the outer coil convolution andthereafter controllably limiting withdrawal of strap from the bubbleregion to the main loop region to thereby effect progressive collapse ofthe strap of the bubble region upon the outer coil convolutionaccompanied by coil tightening rotation of the outer coil'convolution,said braking means comprises a closed hydraulic circuit having pumpingmeans driven by rotation of the traction wheel and flow restrictingmeans determining the resistance to rotation of the traction wheel.

2. In an apparatus for tightening a spiral coil of strap throughrotation of the outer coil convolution in a volute direction, feed meansfor feeding strap, means cooperating with said feed means for formingstrap into a substantially closed strap loop of generally keyslot shapecharacterized by a generally circular main loop region and a generallyU-shaped open bubble region extending outwardly from the main loopregion, retracting means for withdrawing strap of the strap loop, andhold-back mechanism that includes a tractionwheel engageable withbraking means having a predetermined resistance to rotation, thetraction wheel being engageable with the strap of the strap loop at asingle intermediate location therealong and cooperable with theretracting means for tensioning strap of the main loop region to effectfriction clamping engagement thereof with the outer coil convolution andthereafter controllably limiting withdrawal of strap from the bubbleregion to the main loop region to thereby effect progressive collapse ofthe strap of the bubble region upon the outer coil convolutionaccompanied by coil tightening rotation of the outer coil convolution,said hold-back mechanism includes a shiftably mounted frame, an idlerwheel, means for swinging the idler wheel about an axis offset from theplane of the strap loop between a strap pinching position within thebubble region and facing the traction wheel and a retracted positionadjacent the coil and spaced from the bubble region,

and means biasing the frame in a direction to load the idlerwheeltowards the traction wheel, the swinging means includes a hydrauliccylinder and piston mechanism operable after forming of the bubbleregion to swing the idler wheel to the strap inching osition andresponsive durin withdrawal of strap rom the Bubble region to swing theid er wheel to the retracted position, said braking means comprises aclosed hydraulic circuit having pumping means driven by rotation of thetraction wheel and flow restricting means determining the I resistanceto rotation of the traction wheel.

l l l I

1. In an apparatus for tightening a spiral coil of strap throughrotation of the outer coil convolution in a volute direction, feed meansfor feeding strap, means cooperating with said feed means for formingstrap into a substantially closed strap loop of generally keyslot shapecharacterized by a generally circular main loop region and a generallyU-shaped open bubble region extending outwardly from the main loopregion, retracting means for withdrawing strap of the strap loop, andhold-back mechanism that includes a traction wheel engageable withbraking means having a predetermined resistance to rotation, thetraction wheel being engageable with the strap of the strap loop at asingle intermediate location therealong and cooperable with theretracting means for tensioning strap of the main loop region to effectfriction clamping Engagement thereof with the outer coil convolution andthereafter controllably limiting withdrawal of strap from the bubbleregion to the main loop region to thereby effect progressive collapse ofthe strap of the bubble region upon the outer coil convolutionaccompanied by coil tightening rotation of the outer coil convolution,said braking means comprises a closed hydraulic circuit having pumpingmeans driven by rotation of the traction wheel and flow restrictingmeans determining the resistance to rotation of the traction wheel. 2.In an apparatus for tightening a spiral coil of strap through rotationof the outer coil convolution in a volute direction, feed means forfeeding strap, means cooperating with said feed means for forming strapinto a substantially closed strap loop of generally keyslot shapecharacterized by a generally circular main loop region and a generallyU-shaped open bubble region extending outwardly from the main loopregion, retracting means for withdrawing strap of the strap loop, andhold-back mechanism that includes a traction wheel engageable withbraking means having a predetermined resistance to rotation, thetraction wheel being engageable with the strap of the strap loop at asingle intermediate location therealong and cooperable with theretracting means for tensioning strap of the main loop region to effectfriction clamping engagement thereof with the outer coil convolution andthereafter controllably limiting withdrawal of strap from the bubbleregion to the main loop region to thereby effect progressive collapse ofthe strap of the bubble region upon the outer coil convolutionaccompanied by coil tightening rotation of the outer coil convolution,said hold-back mechanism includes a shiftably mounted frame, an idlerwheel, means for swinging the idler wheel about an axis offset from theplane of the strap loop between a strap pinching position within thebubble region and facing the traction wheel and a retracted positionadjacent the coil and spaced from the bubble region, and means biasingthe frame in a direction to load the idler wheel towards the tractionwheel, the swinging means includes a hydraulic cylinder and pistonmechanism operable after forming of the bubble region to swing the idlerwheel to the strap pinching position and responsive during withdrawal ofstrap from the bubble region to swing the idler wheel to the retractedposition, said braking means comprises a closed hydraulic circuit havingpumping means driven by rotation of the traction wheel and flowrestricting means determining the resistance to rotation of the tractionwheel.